Modulation analysis and distortion identification

ABSTRACT

An apparatus, method, computer readable medium, and system are provided to generate a symbol placement associated with a transmission scheme by transforming a retrieved set of equalization coefficients. Symbols included in the symbol placement may be analyzed and quantified in terms of their distance from a decision boundary. Symbols may be synthesized on an iterative basis in order to obtain visibility into the underlying performance of the transmission scheme over time. If equalization is unable to reduce a signal impairment below a threshold value within a predetermined amount of time, then a determination may be made that a non-linear distortion source is present in a network or communication system. Signals received from a plurality of user terminals may be compared with one another in order to determine a probable location or cause of the non-linear distortion.

RELATED APPLICATIONS

The present application is related to, incorporates by reference, andclaims the priority benefit of U.S. Provisional Patent Application No.61/301,835, entitled “Modem Signal Usage and Fault Isolation”, filedFeb. 5, 2010.

FIELD OF ART

The features described herein generally relate to providing users withaccess to content over a network. More specifically, aspects of thedisclosure describe identifying the likely or approximate location of apotential problem or error associated with a network.

BACKGROUND

Service providers and network operators strive to provide qualityservice to users. In the context of networks, signal degradation maypose significant challenges in providing quality service. For example,interference in return path RF frequencies is the most common cause ofupstream transmission failure. Connection-oriented protocols, such asTCP, will typically retransmit lost packets. However, real-timestreaming protocols used in voice and video do not. The loss of upstreampackets results in poor quality voice and video experience from a userperspective. QAM analysis provides a meaningful capability to identifyand resolve return path signal impairments.

Packages composed of hardware and software are available to characterizean upstream communication channel. However, such packages are expensiveto purchase, license and maintain, require specialized skills toinstall, operate and maintain, are band-limited to a finite number ofconnections and require rack space and power, and typically result inuser down-time when hardware is installed or sweeps are in progress.Improved and advanced techniques are needed in order to accurately,efficiently, and quickly characterize upstream communication channels.

SUMMARY

This summary is not intended to identify critical or essential featuresof the disclosure provided herein, but instead merely summarizes certainfeatures and variations thereof.

In some embodiments, pre-equalization coefficients may be used inconjunction with Fourier analysis to derive an inverse channel responseof a return path spectrum. Amplitude-to-frequency and phase-to-frequencydistortion characteristics may be used to synthesize an iteration ofquadrature amplitude modulation (QAM) symbols. The QAM symbols maydemonstrate radial tilt and voltage dispersion caused by underlyingdistortion sources in transmission.

The equalization coefficients may be indicative of samples of a signaltaken at discrete periods of time. Each sample may coincide with a tapof a tap-delay filter. For example, the main-tap may coincide with asignal from a user terminal at a discrete instant in time and the othertaps may represent prior or future samples of the signal relative to themain-tap. In some embodiments, one or more processors associated withone or more devices may execute instructions stored in a memory toimplement the tap-delay filter, to establish equalization coefficients,and to analyze the equalization coefficients.

In some embodiments, a symbol placement associated with a transmissionscheme may be generated or synthesized by transforming the equalizationcoefficients. Symbols included in the symbol placement may be analyzedand quantified in terms of their distance from a (demodulation) decisionboundary. Symbols may be generated on an iterative basis in order toobtain visibility into the underlying performance of the transmissionscheme over time. In some embodiments, if equalization is unable toreduce a signal impairment below a threshold value, then a determinationmay be made that a non-linear distortion source is present in a networkor communication system. Signals received from a plurality of userterminals may be compared with one another in order to determine aprobable location or cause of the non-linear distortion.

Other details and features will also be described in the sections thatfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of this disclosure will become more apparent upon a review ofthe disclosure in its entirety, including the drawing figures providedherewith, the contents of which are fully incorporated herein by way ofreference.

Some features herein are illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements.

FIG. 1 illustrates an example information distribution system.

FIG. 2 illustrates an example architecture, with a closer level ofdetail on one of the premises illustrated in the FIG. 1 network.

FIG. 3 illustrates a logic diagram for demonstrating how to determinevalues for equalization coefficients in connection with one or moreaspects of this disclosure.

FIGS. 4A-4D illustrate constellation diagrams/patterns in connectionwith one or more aspects of this disclosure.

FIGS. 5A-5C illustrate a closer view of a portion of a constellationdiagram in connection with one or more aspects of this disclosure.

FIG. 6 illustrates a representation of maximum symbol energy inconnection with one or more aspects of this disclosure.

FIGS. 7A-7B illustrate examples of equalization coefficients andamplitude distortion in connection with one or more aspects of thisdisclosure.

FIG. 8 illustrates a map in connection with one or more aspects of thisdisclosure.

FIG. 9 illustrates a device suitable for demonstrating one or moreaspects of this disclosure.

FIG. 10 illustrates a method suitable for demonstrating one or moreaspects of this disclosure.

DETAILED DESCRIPTION

It is noted that various connections between elements are discussed inthe following description. It is noted that these connections aregeneral and, unless specified otherwise, may be wired or wireless,direct or indirect, and that this specification is not intended to belimiting in this respect.

FIG. 1 illustrates an example information distribution network 100 onwhich many of the various features described herein may be implemented.Network 100 may be any type of information or content distributionnetwork, such as satellite, optical fiber, coaxial cable, telephone,cellular, wireless, etc. The network may be a hybrid fiber/coaxdistribution network found in many television networks. Such networks100 may use a series of interconnected communication lines 101 toconnect multiple homes 102 to a provider's facility, headend, or centrallocation 103. The central location 103 may transmit downstreaminformation signals onto the lines 101, and each home 102 may have atuner used to receive and process those signals. Signals may alsoinclude upstream transmissions from homes 102 to central location 103.

The lines 101 may be a series of interconnected lines of different type,such as optical fiber and/or coaxial cables, or wireless links. Theremay be one line originating from the central location 103, and it may besplit a number of times to distribute the signal to various remote sitessuch as homes 102 in the vicinity (which may be many miles) of thecentral location 103. The lines 101 may include components notillustrated, such as splitters, filters, amplifiers, etc. to help conveythe signal clearly. Portions of the lines 101 may also be implementedwith fiber-optic cable, resulting in a hybrid fiber/cable (HFC) networkof lines 101. By running fiber optic cable along those portions, signaldegradation in those portions may be significantly minimized, allowing asingle central location 103 to reach even farther with its network oflines 101 than before. Portions of lines 101 may also be implemented viawireless links.

FIG. 2 illustrates a closer view of one of the remote sites, home 102from FIG. 1. As illustrated, the home may be connected to the network100 by, for example, wireless optical fiber or coaxial cable feed 201.The feed may be connected to a gateway device 202, which may serve as aninterface between the devices within the home 102, and the externaldevices out on the network 100. The gateway itself may include tuners,modulators, demodulators, etc. to communicate out on the network 100,and may also include interface components to communicate with thedevices in the home.

As for the network in the home, the specific types of components mayvary, depending on the type of communication network used in the home.One example may be an Internet Protocol network 203 carried over thehome's internal coaxial wiring under the MoCA (Multimedia Over CoaxAlliance) standard. To this end, the gateway 202 may be an IP transportgateway, using IP communications to communicate with the devices in thehome, and with devices outside the home (e.g., via a DOCSIS CMTS in aHFC-type network, for example). Other networks, such as fiber optic orwireless networks, may alternatively be used.

Various devices may communicate on the network in the home. For example,one or more personal computers 204 may use the gateway 202 tocommunicate with other devices on the Internet. Customer premisesequipment (CPE) 205, such as televisions or set-top boxes (STBs), mayreceive IP distribution of video content received at the gateway 202,and convert that video content into a format suitable for display oncorresponding display devices 206, such as televisions, monitors,handheld devices, etc. Alternatively, display devices 206 mayincorporate functionality of premises equipment 205. For example, theCPE 205 may receive an MPEG2 stream of video, and may process thatstream to generate an HDMI (High Definition Multimedia Interface) outputsignal to each CPE 205 or corresponding display device 206. While STBsare described below, one skilled in the art would appreciate thatdevices in addition to, or in lieu of STBs, such as personal computers(PCs), servers, gateways, etc., may be used in some embodiments.

Some display devices in the home, however, might not have their own CPE.Or they might not have the circuitry needed to decode the MPEG2 streamof video received at the gateway 202. For example, display devices suchas televisions 207 a and 207 b might be old-fashioned analogtelevisions, having tuners configured to tune to the analog broadcastchannels defined by the NTSC (National Television System Committee). Orthey may be digital televisions not equipped to receive and decode thelatest form of digital compression or modulation used on the network100. To support such legacy devices, the gateway 202 may include a localwireless transmitter 208.

The local wireless transmitter 208 may be configured to transmit alow-power radio frequency channel carrying video signals of a selectedprogram for local reception within the home. For example, if thetelevision 207 a is an analog television, the gateway 202 may use thetransmitter 208 to transmit a selected program as an NTSC video signalon an NTSC Channel (e.g., channel 2). That channel and signal can betuned by the television 207 a, and displayed for the user's consumption.In this manner, legacy devices may continue to be used even iftransmission techniques advance. The transmitter 208 may use any desiredwireless format, such as IEEE 802.11, ZIGBEE, BLUETOOTH, etc. An 802.11transmitter 208 may be especially useful, since the 2.4 GHz range ofthat standard happens to overlap the 300 MHz-3 GHz frequency range ofthe NTSC UHF channels.

Any number and type of devices (e.g., computers, mobile devices, modems,telephones, set top boxes, etc.) may be located within the network ofFIGS. 1 and 2. Those devices located at a user's premises, such as home102, may generally be referred to as user terminals.

By way of introduction, FIG. 3 illustrates a simplified logic diagramconnecting a user terminal, such as a computer or modem, to anotherdevice, such as a termination system (TS). In FIG. 3, the user terminaltransmits a signal 302 (e.g., a square wave) to the TS. In an idealoperating environment, upon receipt at the TS, signal 308 would beidentical to signal 302. However, as shown in FIG. 3, signal 308includes ripple not present in signal 302 due to distortion. Thedistortion may be present in the communication channel (e.g., due to animpedance cavity as illustrated via components 320) coupling the userterminal and TS, or the source of the distortion may be present in oneor both of the user terminal and the TS. In any event, the TS mayprovide the user terminal with a set of channel coefficients(illustrated as signal 314 in FIG. 3) that correspond to the inverse ofthe frequency response associated with the communication from the userterminal to the TS. In this manner, the user terminal may pre-distortfuture signal transmissions, such that when the signals are received atthe TS, the received signals are ideal in terms of amplitude and phaseover the operating frequency range.

Given that the frequency response associated with the communicationchannel or devices may change over time, a new or updated set ofcoefficients may be communicated to the user terminal periodically(e.g., once every thirty seconds). This periodic update may be scheduledto occur when the user terminal is in an idle state. In someembodiments, the TS may analyze predetermined data fields associatedwith each, or a subset of every, data transmission from the userterminal for purposes of updating the coefficients.

The equalization coefficients may be useful for correcting lineardistortions. Linear distortions may be those distortions that impact theamplitude and/or phase of an original signal and tend to generally bepresent over time. Micro-reflections (which, as seen by a receiver, maybe a copy of a transmitted signal arriving late and with a reducedamplitude), amplitude distortion (which may represent undesirablevariation in a communication channel's amplitude response and may resultin distortion of a signal's amplitude), and group delay variation (whichmay represent undesirable variation in a communication channel's phaseresponse and may result in distortion of a signal's phase or a variationin the propagation of frequency components of the signal across thechannel) are examples of linear distortions. Non-linear distortions maybe those distortions that generate distortion components, includingharmonics of the original signal or multiples of the original signalwith other energy present in a return band. Examples of non-lineardistortions are ingress and noise. Techniques for detecting and handlinglinear and non-linear distortions are described further below.

As described in the incorporated U.S. Provisional Patent Application No.61/301,835, a data collection apparatus may be used to retrieve orgather pre-equalization coefficients from one or more devices (e.g.,user terminals (such as modems), a server, a termination system (TS)such as a cable modem termination system (CMTS), etc.). The coefficientsmay be parsed, normalized, and analyzed using Fourier transformation toderive amplitude and phase components. The amplitude and phasecomponents can be derived from a time domain representation, which canbe used to synthesize or approximate a symbol placement in connectionwith a transmission scheme. For example, in the context of conveyingsymbols using quadrature amplitude modulation, such as 64-QAM, every bitpattern corresponding to the sixty-four (64) possible symbols can besynthesized. Multiple (e.g., a number ‘n’) iterations can be conductedto achieve a (gaussian) scatter. Such techniques may be applied withrespect to a single communication channel (e.g., in relation tocommunications from a first device, such as a user terminal, and asecond device, such as a TS). The techniques may also be applied acrossa plurality of communication channels or devices (e.g., multiple userterminals in communication with one or more other devices, such as aTS). For example, an in-home service repairman or installer may beinterested in the channel characteristics associated with a particularuser terminal, whereas a line operator may be more concerned with theperformance of all (or a subset of) the user terminals in thecommunication system.

FIGS. 4A-4D (collectively referred to as FIG. 4) illustrate a (64-QAM)constellation pattern that may be used to represent the impact thatdistortion has in terms of demodulated symbol recognition/detection at areceiver. FIG. 4A represents an ideal symbol placement when nodistortion sources are present. As shown in FIG. 4A, the symbols (two ofwhich are labeled as 402 a-1 and 402 a-2) reside at the center of eachof the sixty-four (64) boxes (two of which are labeled 408 a-1 and 408a-2).

FIGS. 4B and 4C represent the effect of phase and amplitude distortion,respectively, on the demodulated symbols. Phase distortion is frequentlydescribed in terms of group delay distortion, which represents thechange in the phase of a signal relative to the frequency components ofthe signal. When group delay distortion is present, the frequenciestransmitted in the system or network are not transmitted in the sameamount of time—that is, with equal time delay. For example, in thecontext of equalizer coefficients implementing a bandpass filter, thedelay may be less towards the center of the filter's passband relativeto the filter's band edges. Amplitude distortion relates to a change ofthe magnitude of a received signal relative to the magnitude of thetransmitted signal. If the magnitude of the received signal is largerthan the magnitude of the transmitted signal, then the distortion issaid to be constructive in nature. Conversely, if the magnitude of thereceived signal is less than the magnitude of the transmitted signal,then the distortion is said to be destructive in nature.

FIG. 4D represents a typical symbol placement in the presence ofdistortion, taking into consideration both phase and amplitudedistortion. Relative to the ideal symbol placement in FIG. 4A, thesymbols in FIG. 4D do not reside in the exact centers of each of thesixty-four (64) boxes. Instead, as shown in FIG. 4D, the symbols take ona scattered appearance and may be characterized by ascatter-distribution function. A result of this scatter is a reductionin terms of noise margins associated with the decision boundaries (e.g.,the perimeters) of each of the sixty-four (64) boxes, which increasesthe likelihood of incurring a symbol error at the receiver.

The description provided above in connection with FIGS. 4A-4D relates tothe use of a 64-QAM modulation scheme. Other n-QAM schemes (e.g.,16-QAM, 256-QAM, etc.) may be used in some embodiments. In someembodiments, other modulation schemes (e.g., amplitude modulation,frequency modulation, etc.) may be used in addition to, or as analternative for, n-QAM.

In terms of the constellation patterns shown in FIGS. 4A-4D, a symbol'slocation may be referenced by its in-phase and quadrature components.FIGS. 5A-5C (collectively referred to as FIG. 5) illustrate one (1) ofthe sixty-four (64) boxes of FIGS. 4A-4D. As shown in FIG. 5, thein-phase (I) component resides along the vertical axis, and thequadrature (Q) component resides along with horizontal axis. FIG. 5 isillustrative; other coordinate or reference systems may be used in someembodiments.

FIG. 5A illustrates an ideal symbol location indicative of either a lackof distortion or the presence of distortion sources that cancel oneanother out. In the presence of amplitude distortion, the symbol wouldtend to move closer to the ‘Q’ axis (relative to the ideal symbolplacement) as shown in FIG. 5B. In the presence of phase distortion, thesymbol would tend to move closer to the ‘I’ axis (relative to the idealsymbol placement) as shown in FIG. 5C.

FIGS. 4 and 5 are representations of the symbol locations as provided ina constellation pattern for purposes of visualizing the symbol-space. Acalculation of a modulation error ratio (MER) may be conducted inconjunction with the constellation patterns of FIGS. 4 and 5 tocharacterize symbol placement. Modulation error ratio may represent theratio of average symbol power to average error power. An equation forcalculating MER is as follows:

${{MER}\mspace{14mu}({dB})} = {{- 10}*\log\; 10\{ \frac{\sum\limits_{i = 1}^{n}( {{\delta\; I_{i}^{2}} + {\delta\; Q_{i}^{2}}} )}{\sum\limits_{i = 1}^{n}( {I_{i}^{2} + Q_{i}^{2}} )} \}}$where${\delta\; Q} = \sqrt{\sum\limits_{i = 1}^{n}\frac{( {{A_{i}\sin\;\alpha_{i}} + {\phi_{i}\cos\;\alpha_{i}}} )^{2}}{n}}$${\delta\; I} = \sqrt{\sum\limits_{i = 1}^{n}\frac{( {{\phi_{i}\sin\;\alpha_{i}} + {A_{i}\cos\;\alpha_{i}}} )^{2}}{n}}$

In terms of the MER equation shown above, the in-phase (I) andquadrature (Q) components of the ideal symbol placements are known basedon the modulation scheme used. A Fourier transform computation providesthe inverse distortion of the amplitude (A) and phase (Φ) respective offrequency. A root-mean-square (RMS) calculation of the amplitude andphase distortion provides the in-phase delta (δI) and quadrature delta(δQ) values for each symbol (n), where α represents the amplitude/phasevector angle (radius). Using the MER equation, a quantified value may beobtained that may be used, for example, to determine how to prioritizeresolving (potential) problems or issues. For example, a networkoperator or provider may allocate resources (e.g., personnel and toolsets) to those portions of a network having the lowest MER (and thus,the highest average error power relative to the average symbol power).

The difference between the ideal symbol location at the center of agiven box and the actual location of the symbol is referred to as anerror vector. The distance from the center of the box may be referred toas the error vector magnitude (EVM). The EVM may be calculated asfollows:

${EVM} = {100\%*\sqrt{\frac{\frac{1}{n}{\sum\limits_{i = 1}^{n}( {{\delta\; I_{i}^{2}} + {\delta\; Q_{i}^{2}}} )}}{{SE}^{2}}}}$

The terminology used in the EVM equation is the same as the terminologydiscussed above with respect to the calculation of MER. ‘SE’ representsthe maximum symbol energy and is calculated from the outer corners of anI-Q constellation as shown in FIG. 6. SE²=I² _(max)+Q² _(max), whereI_(max) is the real component of the outermost constellation symbol inthe constellation diagram, Q_(max) is the imaginary component of theoutermost constellation symbol in the constellation diagram, and theoutermost constellation symbol is the symbol with the highest power.

The above-described techniques are effective in determining the impactof linear distortion on symbol placement. Stated in a slightly differentway, the above techniques may be used to quantify the impact that lineardistortion sources have on symbol placement. Linear distortions may betransformative in nature and may create standing-wave types ofimpairments. The linear distortions may be accounted for bypre-distorting transmissions from the user terminal in accordance withthe inverse channel response associated with the communication system.For example, equalization coefficients may be used to pre-distort asignal transmission from a user terminal to a TS on an upstreamcommunication channel.

As described above, non-linear distortion sources (e.g., ingress andnoise) may also be present in a communication network. Whereas thelinear distortions may tend to be transformative in nature, non-lineardistortion sources may tend to be additive in nature. Use of apre-distorting mechanism (such as equalization coefficients) may help tomitigate the effects of the non-linear distortion in terms of symboldemodulation/recognition at a receiver. However, the use of apre-distorting mechanism may also tend to increase or amplify theeffects of the non-linear distortion in terms of symboldemodulation/recognition at a receiver.

Given that non-linear distortion sources may be spurious or intermittentin nature, a technique may be used to determine the likely presence of anon-linear distortion. For example, as described in the incorporatedU.S. Provisional Patent Application No. 61/301,835, standing wave andsteady-state interference that may be indicative of a linear distortionmay typically be equalized within a relatively short period of time(e.g., 30 seconds). Non-linear distortions, such as noise, common pathdistortion (CPD) and impulse may demonstrate a frequency responsesignature that never completely equalizes. Equalization coefficients maybe collected, subjected to a Fourier transformation, and analyzed in theaggregate for signal impairments. Amplitude, group and phase delay maybe measured for Voltage Standing Wave Ratio (VSWR) or any other type ofparameter to quantify a wave magnitude or ratio.

If subsequent equalization (by way of coefficient replacement orcoefficient combination techniques, such as averaging or convolution)fails to reduce the wave ratio, this may indicate the presence ofnon-linear distortion sources.

The likely existence of a non-linear distortion source may be determinedbased on whether equalization eliminates or reduces a wave ratio valuewithin a predetermined amount of time (e.g., within a relatively shortamount of time). Furthermore, techniques described herein can also beused to provide an approximate location of the non-linear distortionsource. Stated in a slightly different way, each user terminal'scontribution to the distortion can be analyzed and determined.

FIG. 7A illustrates an example of sets of equalization coefficients fora plurality of user terminals (e.g., modems) as obtained from a TS. Inparticular, FIG. 7A shows twenty-four (24) taps along the horizontalaxis, and amplitudes corresponding to each of the taps on the verticalaxis. As shown, the majority of the energy of the signals is located inthe reference or main-tap position #8. FIG. 7B represents the signalsreceived from the user terminals in terms of amplitude (along thevertical axis) relative to frequency (along the horizontal axis). Amajority of the received signals reside within ±0.5 band of 0.0 dBc asshown (as indicated by the heavier, darker bands near 0.0 dBc), and islikely indicative of effective equalization of any linear distortionsource(s) that may have been present. Some of the received signalsdemonstrate large magnitudes and changes in terms of amplitude, whichmay be indicative of a non-linear distortion, as shown. While not shownin FIG. 7, a plot of the phase (similar to that shown in FIG. 7B foramplitude) could also be generated and analyzed.

An analysis may be conducted to identify the user terminals that appearto be subject to non-linear distortion. For example, a device (such as aTS) may maintain a table of responses with an entry for each userterminal, where each user terminal or device may be identified by anidentifier, such as a MAC address. Once the user terminals have beenidentified, relationships between the terminals can be formulated orpostulated in an effort to pinpoint the source of the non-lineardistortion. For example, FIG. 8 illustrates a scenario where theidentified user terminals are correlated to their geographic location(e.g., by way of user account information). In the scenario depicted inFIG. 8, all of the user terminals that are subject to non-lineardistortion are located within circle 802. Armed with the knowledge ofthe geographic location(s) impacted by the non-linear distortion, alayout specific to the impacted terminals may be analyzed (e.g.,compared) to determine the likely source(s) of the non-lineardistortion. In the scenario associated with FIG. 8, all of the userterminals located within circle 802 may be connected to a TS by way ofan amplifier 904 near the corner of Church Street and Webster Street asshown in FIG. 9.

The scenarios depicted in FIGS. 7-9 are illustrative. Distortion sources(particularly non-linear distortion sources such as ingress and noise)may cause signal impairments that may manifest themselves in any numberof ways, in networks of various topologies or layouts. The techniquesdescribed herein may provide a starting point or baseline for diagnosingan issue or problem by prioritizing where to look first. Based on theforegoing description, a line operator or technician may be able todetermine or pin-point the likely location of a non-linear distortionsource without having to have knowledge of the internal configuration ofthe user terminals or the TS. Problems or issues that previously wouldhave remained unresolved, or taken teams of personnel weeks or evenmonths to fix, may be reduced to a simple task conducted by a singleperson taking on the order of half an hour.

FIG. 10 illustrates a method that may be used to practice one or moreaspects of this disclosure. In step 1002, equalization coefficients maybe retrieved and analyzed to determine a communication channel'samplitude and/or phase response over an operating frequency range. Theequalization coefficients may be obtained from a user terminal, from aTS, from a storage device (e.g., a database), or any other device thatmay be used to store the equalization coefficients.

In step 1010, a symbol placement may be generated or synthesized basedon the coefficients retrieved and analyzed in step 1002. In this manner,service personnel, a line operator, analyses software, or the like mayobtain insight into the underlying performance of themodulation/demodulation from a pre-equalization perspective. Moreover,such a symbol generation lends itself to testing all possiblecombinations of symbols without having to actually exercise theassociated hardware/software/firmware (e.g., without having to actuallytransmit or receive those symbols). Constellation diagrams similar tothe ones shown in FIGS. 4B-4D may be generated and/or displayed on adisplay device in conjunction with step 1010.

While not shown in FIG. 10, multiple iterations of coefficientretrieval/analysis (step 1002) and symbol generation (step 1010) may beconducted over time to obtain a scatter of transmission performance overtime. Such multiple iterations may be conducted using a time-based loopin a program executing on one or more computers or computing platforms.

In step 1018, a determination may be made whether the equalization iseffective in reducing distortion (in terms of amplitude and/or phase)over a (predetermined period of) time. For example, equalization mayhave a tendency to average-out signal distortions caused by a lineardistortion source. If the equalization is ineffective in eliminating orreducing the distortion below a threshold level within a thresholdamount of time, a determination may be made that it is likely orprobable that a non-linear distortion source is present.

In step 1026, signals received from a plurality of user terminals may beanalyzed (e.g., compared) in an effort to establish a relationshipbetween those user terminals that may be experiencing signal impairmentabove a threshold level. For example, as described above with respect toFIGS. 7-9, a geographic location of user terminals experiencing signalimpairment above a threshold level may be determined, and a networktopology may be studied or compared to determine what those userterminals have in common relative to those user terminals that are notexperiencing the signal impairment. In this manner, probable or likelysource(s) of the non-linear distortion may be identified.

In step 1034, one or more status messages may be generated. The statusmessage may indicate those symbols that are most likely to be subject todemodulation error at a receiver. For example, the equalizationcoefficients may be analyzed to determine which pre-equalization symbolsare closest to or within a threshold distance of the decision boundariesassociated with the transmission scheme used. In this manner, a (sub)setof candidate input symbols may be generated to facilitate testing ortroubleshooting in the event of a reported error or failure.

The status message(s) of step 1034 may also provide a distance from auser terminal (or TS) to a likely source of a problem. For example, amap similar to the one shown in FIG. 8 may be generated. In this manner,network management may be in a better position to determine the extentof a potential problem and the personnel and tools that may need to beallocated to address the potential problem. If the topology of thenetwork or communication system is known in sufficient detail, thedistance may be correlated to device(s) located at that distance. Forexample, in reference to FIG. 9, the status message may provide detailsregarding amplifier 904, such as amplifier 904's make and model number,its version/revision number, and any other information that may beuseful in analyzing or troubleshooting the amplifier 904.

The status message(s) generated in step 1034 may include additionalinformation that may be used to facilitate debugging or troubleshooting.For example, the TS may maintain a library or database of past issues orproblems (with possible input from service personnel or the like) andthe causes of those past problems. In this manner, the library ordatabase may be consulted to identify not only the likely location ofthe problem or error, but the likely cause of the problem or error,thereby correlating a current issue with past issues and techniques usedto resolve those past issues.

Having such knowledge in advance of going to the site of the problem mayenable service personnel to pack appropriate tool sets and mayfacilitate the selection of service personnel (e.g., if correcting theproblem entails a specific skill set, one service technician could beselected over another).

The status message(s) generated in step 1034 may be conveyed in one ormore formats. For example, the status message may include an audiomessage (e.g., a broadcast over radio), an email, a text message, animage/video message, or the like. If a potential problem is located inthe user's premises (e.g., the user's home), the status message may beconveyed to the user and may either request the user to schedule anappointment with service personnel, or if the problem is simple enoughto correct (e.g., a loose connector), may provide the user with guidance(e.g., an instructional video) on how to fix the problem (e.g., how toalter a user terminal or a component associated with the user terminal).

While the above description was largely presented in the context of userterminals in communication with a TS, aspects of this disclosure mayreadily be applied to other contexts as well. For example, the qualitiesof peer to peer communication systems, (mobile) telephone communicationsystems, satellite communication systems, and the like may also bemonitored and evaluated using the techniques described herein. Ofcourse, the contexts described herein are merely illustrative.Additional contexts are well within the scope and spirit of thisdisclosure.

Although not required, various aspects described herein may be embodiedas a method, a data processing system, or as a computer-readable mediumstoring executable instructions. Accordingly, those aspects may take theform of an entirely hardware embodiment, an entirely softwareembodiment, an entirely firmware embodiment, or an embodiment combiningsoftware, firmware and hardware aspects. The functionality may beresident in a single computing device, or may be distributed acrossmultiple computing devices/platforms, the multiple computingdevices/platforms optionally being connected to one another via one ormore networks. In addition, various signals representing data or eventsas described herein may be transferred between a source and adestination in the form of electromagnetic waves traveling throughsignal-conducting media such as metal wires, optical fibers, and/orwireless transmission media (e.g., air and/or space). In someembodiments, one or more transitory and/or non-transitory media mayinclude instructions that, when executed by one or more computers orapparatuses, cause the one or more computers or apparatuses to performthe methodological acts and processes described herein.

As described herein, the various methods and acts may be operativeacross one or more computing servers and one or more networks. Thefunctionality may be distributed in any manner, or may be located in asingle computing device (e.g., a server, a client computer/userterminal, etc.). As discussed herein, timing and frequency informationrelated to communications between two or more devices may be obtainedacross various data, television, telephone, and computer networks, andboth proactive and reactive support in the presence of potentialproblems or actual errors is provided for. Moreover, upstream spectrumanalysis capabilities are provided to operations and support personnelwho would not normally have access to analyzer hardware. Visibility intoupstream channels may be obtained without added expense. The analysisinto the upstream channel performance may be conducted on a non-invasivebasis, thereby eliminating or mitigating impact on user service. Forexample, service personnel (or other persons) may obtain insight intothe relative health and performance of the modulation/demodulationwithout having to turn off an equalizer or equalizer functionality at auser terminal. The techniques described may be used to determine thelikely existence of a non-linear distortion source and its location.Moreover, the techniques described herein may require fewer resources(e.g., service personnel, tool sets, etc.) relative to the techniquesthat were previously used.

As described herein, the methodological acts and processes may be tiedto particular machines or apparatuses. For example, as described herein,a user terminal, such as a STB, computer, or modem, may equalize asignal prior to transmitting the signal to a receiving device (e.g., aTS). The coefficients used to perform that equalization may be(repeatedly) retrieved and analyzed from one or both of the userterminal and the receiving device. More generally, one or more computersmay include one or more processors and memory storing instructions, thatwhen executed, perform the methodological acts and processes describedherein. Furthermore, the methodological acts and processes describedherein may perform a variety of functions including transforming anarticle (e.g., equalization coefficients in conjunction with a receivedsignal) into a different state or thing (e.g., a likelihood of a symbolerror or a measurement of how hard an equalization function is workingat a user terminal to eliminate distortion, a synthesis of symbolplacement in relation to a modulation/demodulation scheme used, a likelyor approximate location of a potential problem or error, etc.).

The various embodiments and examples described above are, as stated,merely examples. Many variations may be implemented to suit a particularimplementation, and the various features may be combined, divided,rearranged, omitted and/or augmented as desired. The scope of thispatent should not be limited by any of the specific examples describedherein.

What is claimed is:
 1. A method comprising: retrieving a first set ofequalization coefficients; and generating, by a computing device, asymbol placement associated with a transmission scheme based on thefirst set of equalization coefficients; retrieving a second set ofequalization coefficients subsequent to retrieving the first set ofequalization coefficients; and updating the symbol placement associatedwith the transmission scheme responsive to retrieving the second set ofequalization coefficients.
 2. The method of claim 1, further comprising:generating a constellation pattern based on the symbol placement.
 3. Themethod of claim 2, further comprising: displaying the generatedconstellation pattern on a display device.
 4. The method of claim 1,further comprising: transmitting to a user terminal, based on thegenerated symbol placement, at least one of: (1) a request to schedulean appointment, and (2) guidance on how to alter the user terminal or acomponent associated with the user terminal.
 5. The method of claim 1,further comprising: calculating at least one of a modulation error ratio(MER) and an error vector based on the symbol placement.
 6. The methodof claim 1, further comprising: quantifying a distortion present in acommunication channel in terms of at least one of amplitude over anoperating frequency range and phase over the operating frequency range.7. The method of claim 1, further comprising: calculating, for at leastone of a plurality of generated symbols included in the symbolplacement, at least one distance relative to at least one of a pluralityof corresponding ideal symbols; and displaying the at least onecalculated distance.
 8. A method comprising: determining thatequalization is unable to reduce, within a predetermined amount of time.a signal impairment associated with a signal received from a userterminal below a threshold value; and determining that a non-lineardistortion source is present in a communication channel connected to theuser terminal responsive to said determining that the equalization isunable to reduce the signal impairment associated with the signalreceived from the user terminal below the threshold value within thepredetermined amount of time.
 9. The method of claim 8, furthercomprising: determining that equalization is unable to reduce, withinthe predetermined amount of time, a plurality of signal impairmentsassociated with a plurality of signals received from each of a pluralityof user terminals below the threshold value, the plurality of userterminals including the user terminal; and comparing a layout associatedwith the plurality of user terminals relative to a layout associatedwith at least one other terminal to determine a probable location of thenon-linear distortion source, wherein a signal received from the atleast one other terminal is not impaired above the threshold value. 10.The method of claim 9, further comprising: generating at least onestatus message comprising a map identifying a geographic region wherethe plurality of user terminals are located.
 11. The method of claim 9,further comprising: generating at least one status message comprising anidentification of at least one device located at the probable locationof the non-linear distortion source.
 12. An apparatus comprising: atleast one processor; and memory storing instructions that, when executedby the at least one processor, cause the apparatus to: retrieve a set ofequalization coefficients; generate, based on the set of equalizationcoefficients, a symbol placement associated with a transmission scheme;and transmit to a user terminal, based on the generated symbolplacement, at least one of: (1) a request to schedule an appointment,and (2) guidance on how to alter the user terminal or a componentassociated with the user terminal.
 13. The apparatus of claim 12,wherein the instructions, when executed by the at least one processor,cause the apparatus to: generate a constellation pattern based on thesymbol placement.
 14. The apparatus of claim 13, further comprising: adisplay device, wherein the instructions, when executed by the at leastone processor, cause the apparatus to: display the constellation patternon the display device.
 15. The apparatus of claim 12, wherein theinstructions, when executed by the at least one processor, cause theapparatus to: calculate at least one of a modulation error ratio (MER)and an error vector based on the symbol placement.
 16. The apparatus ofclaim 12, wherein the instructions, when executed by the at least oneprocessor, cause the apparatus to: quantify a distortion present in acommunication channel between the apparatus and the user terminal interms of at least one of amplitude over an operating frequency range andphase over the operating frequency range.
 17. The apparatus of claim 12,wherein the transmission scheme comprises quadrature amplitudemodulation.
 18. The apparatus of claim 12, wherein the instructions,when executed by the at least one processor, cause the apparatus to:identify a subset of symbols included in the symbol placement that arewithin a threshold distance of one or more decision boundaries.
 19. Theapparatus of claim 12, wherein the instructions, when executed by theleast one processor, cause the apparatus to: retrieve a second set ofequalization coefficients subsequent to retrieving the set ofequalization coefficients; and update the symbol placement associatedwith the transmission scheme responsive to retrieving the second set ofequalization coefficients.